Codecs are a crucial component of modern communication systems, including cellular communication systems, for compressing digitized voice and video signals prior to transmission and decompressing the compressed signals upon reception. G.711 is an ITU-T standard for audio companding released in 1972, and uses a pulse code modulation technique to provide narrow bandwidth (≈4 kHz) toll quality audio in the range of 300 Hz to 3400 Hz at a data rate of 64 Kbit/s. Legacy G.711 networks continue in operation to communicate voice and digital information such as fax and acoustic modem data on public switched landline networks. The Adaptive Multi-Rate (AMR) codec standardized in 3GPP, has a bandwidth (≈4 kHz) similar to G.711, provides an adaptive rate narrowband audio codec and is used in existing 2G, 3G and 4G cellular voice networks. G.722.2 is an ITU-T standard and provides an Adaptive Multi-Rate WideBand (AMR-WB) codec for cellular networks and implements a wider bandwidth than AMR. “HD Voice” is implemented using AMR-WB and has a wider bandwidth (≈8 kHz) than toll quality voice and occupies a bandwidth range of 50 Hz to 7000 Hz. An IETF standard RFC 6716 defines the OPUS codec, which provides an adaptive rate codec with a maximum bandwidth wider than HD voice, having a full audio bandwidth (≈20 kHz) which occupies a bandwidth range of 20 Hz to 20 kHz. OPUS has the ability to change the audio bandwidth to adapt to changing network conditions, unlike AMR-WB and AMR.
If either or both near-end and far-end cell phones are configured for the narrower bandwidth AMR codec, then both cell phones select the narrower bandwidth codec. This selection may occur because one or both cell phones are only equipped with an AMR codec or one or both wireless links to a corresponding cellular tower network is limited to supporting only AMR. In this situation the audio profile of both cell phones is set for a narrower bandwidth voice signal.
If both near-end and far-end cell phones are equipped with AMR-WB codecs and the cell towers and corresponding wireless network links facilitate HD voice, then each cell phone negotiates the use of the AMR-WB codec and the wider bandwidth. The audio profile of each cell phone is configured for the wider bandwidth and an official HD voice logo may be rendered on the cell phone display. In this situation callers enjoy both a wider bandwidth higher quality audio signal than the narrower bandwidth audio signal provided by an AMR codec as well as the social status enhancement associated with a cell phone that renders the HD voice logo.
However, in some implementations even though both cell phones and both wireless networks coupled to the cell phones are capable of facilitating HD voice, an intervening network linking near-end and far-end networks may only be capable of toll quality voice. Since the intervening network communicates data used for cell phone codec negotiation, the cell phones detect that both have HD voice codecs and both networks links support HD voice, so HD voice communication is negotiated, the corresponding wider bandwidth audio profile selected and HD voice icon rendered. In this case however, the HD voice is transcoded into narrower bandwidth toll quality voice for communication through the intervening network and transcoded back to HD voice. Thus, both cell phones are properly configured for HD voice in accordance with negotiations facilitated by the networks associated with the cell phones, but the bandwidth is limited to toll quality voice because of the transcoding processes of an intervening network. Consequently the bandwidth of the audio signal between the cell phones is not matched to the codec bandwidth negotiated by the cell phones. This mismatch results in degraded audio, which has been described as “muddy”. The muddy audio may actually sound worse than narrower bandwidth AMR because the wider bandwidth audio profile of HD voice does not filter out undesirable components that would otherwise be filtered if the audio profile was configured for narrower bandwidth audio. To compound matters, the degraded audio is produced while the HD voice icon is rendered.
This condition inappropriately reflects negatively on cell phone manufacturers and results in customer dissatisfaction, complaints and reduction in good will and customer loyalty. Often times users of the cell phones complain to the cell phone manufacturer about the reduced audio quality produced by their otherwise well-constructed and properly operating equipment. The customer has paid for a high quality audio signal but is not experiencing a high quality audio signal. Even more, the cell phone icon indicates a high quality audio signal is indeed being delivered. Nevertheless, the cell phone is operation properly in accordance with established conventions and requirements, and nothing can be done by a cell phone manufacturer to restore bandwidth losses introduced by intervening networks during the cell phone call.
Unlike legacy codecs such as G.711, AMR and AMR-WB, more modern audio codecs such as OPUS are able to adapt to network congestion by adapting the bandwidth of the audio signal when appropriate. However, the corresponding audio quality can occasionally change significantly during the duration of a call because of the adapting of the bandwidth. This occurs even when both cell phones use the same adaptive rate codec and a corresponding icon is rendered on the display indicative of the full bandwidth adaptive rate codec.